The technology of the disclosure generally relates to managing optical sources in distributed communication systems and more particularly to managing laser diodes.
Wireless communication is rapidly growing, with ever-increasing demands for high-speed mobile data communication. As an example, so-called “wireless fidelity” or “WiFi” systems and wireless local area networks (WLANs) are being deployed in many different types of areas (e.g., coffee shops, airports, libraries, etc.). Distributed communication systems (one type of which is a distributed antenna system) communicate with wireless devices called “clients,” which must reside within the wireless range or “cell coverage area” to communicate with an access point device.
One approach to deploying a distributed antenna system (DAS) involves the use of radio frequency (RF) antenna coverage areas, also referred to as “antenna coverage areas.” Antenna coverage areas typically have a radius in the range from a few meters up to twenty meters. Combining a number of access point devices creates an array of antenna coverage areas. Because the antenna coverage areas each cover small areas, there are typically only a few users (clients) per antenna coverage area. This arrangement allows for minimizing the amount of RF bandwidth shared among the wireless system users.
One type of DAS distributes RF communication signals over optical fibers. A DAS can include head end equipment (HEE) optically coupled to remote units (RUs) or remote antenna units (RAUs) having an antenna to provide antenna coverage areas. The RUs have RF transceivers coupled to one or more antennas to wirelessly transmit RF communication signals. The antennas in the RUs also receive RF signals from clients in the antenna coverage area which are sent over optical fiber to the HEE.
Optical signals are placed onto the optical fibers by laser diodes such as the QF9550CM1 Quantum Cascade Laser sold by THORLABS of Newton, N.J. The optical power of the laser diode is proportional to the electrical current that drives the laser diode. System designers expect the power received at the RUs to fall within a certain band, for example, 14 dBm to 17 dBm. To maintain the received power within the desired range, the overall gain of the system is estimated during system setup by injecting a known signal at the transmitter and measuring the signal at the receiver. The measured value is returned to the transmitter and an estimate of the overall gain is stored. Based on the overall gain of the system, the power level needed at the laser diode may be calculated. While such calibration provides a good first order estimate of the overall gain of the system, environmental factors may cause variations for which the calibration does not compensate. Accordingly, there remains a need to improve the model of the system and provide the appropriate gain.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.